1. Field of the Invention
The present invention relates to reciprocating power tools, and more particularly, to a piston retaining system in the barrel of a pneumatic tool.
2. Description of the Prior Art
Reciprocating power tools that hammer, chisel, and drill have been utilized in the construction industry for years, and will likely continue to play an important role on most job sites in the future. Pneumatically driven reciprocating tools have proven to be particularly effective in delivering high performance for relatively low cost. While ongoing design improvements have enhanced certain functional aspects of such tools, the basic design concept of a reciprocating pneumatic tool has not changed.
An example of such a tool is the Chicago Pneumatic(trademark) 4181(trademark) xe2x80x9cRivet Buster.xe2x80x9d Like most similar pneumatically driven tools, the 4181 includes an elongated barrel with a handle and trigger at one end and a retaining sleeve at the other end for holding a workpiece (e.g., a chisel or the like). Inside an upper portion of the barrel, proximate the handle, is a piston that reciprocates back and forth within the barrel, repeatedly striking the butt end of the workpiece within the lower portion of the barrel, thereby causing the workpiece head to reciprocate outside of the barrel.
As noted above, such tools include a retaining sleeve, which may be removed to perform routine maintenance on the tool or to remove or replace the workpiece. In tool designs like the 4181, once the sleeve, workpiece and collars are removed, the piston can, under certain conditions, freely escape from the barrel. This feature promotes easy removal of the piston which may be desirable for maintenance purposes. Moreover, as long as the user takes basic precautionary steps, such as disengaging the tool from the air supply before removing the sleeve, the design presents no problem. However, if the worker fails to take such precautions, the piston could inadvertently exit the barrel. For example, if the sleeve is removed and the trigger is pressed while the tool is operable, the piston could be ejected from the barrel with a fair amount of force, causing damage.
Thus, a need exists to provide a system that will prevent the free escape of the piston from the barrel when the retainer sleeve is removed. In addition, the system should not interfere with the existing functionality of the tool.
In order to overcome the limitations of the prior art, the present invention provides a piston retaining system for preventing the free escape of the piston from the barrel of a reciprocating tool when the retaining sleeve and workpiece are removed. The improved tool comprises a barrel, a piston slidably placed within an upper portion of the barrel, a retaining sleeve mounted proximate a lower portion of the barrel, a workpiece slidably retained within the lower portion of the barrel by the retaining sleeve, and a piston retaining system including at least a first, a second and a third piston retaining mechanism, for preventing the free escape of the piston from the barrel when the retaining sleeve and workpiece are removed. The retaining mechanisms are mounted within the lower portion of the barrel in such a manner that neither the piston nor the workpiece contacts the retaining mechanisms during the actual operation of the tool.
The first piston retaining mechanism may comprise a retainer ring placeable within a circular groove cut into the inside diameter of the barrel. Specifically, the retainer ring is distally mounted around the butt of the workpiece. The retainer ring includes an opening with a diameter greater than the diameter of the butt of the workpiece, and slightly smaller than the first end of a stepped piston, and significantly less than the largest diameter of the piston. Therefore, the tool can operate without interference from the ring, yet the ring acts as a brake when engaged by the lower portion of the piston, and further, prevents the piston from exiting the barrel when the retaining sleeve and workpiece are removed. The ring may include a tapered inner surface to help trap the piston if required. The ring may be made of strong, yet flexible material, with a scarf cut so that it can be removed from the barrel and replaced if necessary.
The second piston retaining mechanism may include a restricted area formed within the lower end of the barrel. The restricted area has a diameter greater than the diameter of the butt of the workpiece and the first stepped end of the piston, but less than the largest diameter of the piston. The restricted area prevents the inadvertent escape of the piston in the event the ring is worn, removed or in some other manner malfunctions while the retaining sleeve and workpiece are removed.
The third piston retaining mechanism may include an annular ring located within the lower end of the barrel, beyond the location of the second piston retaining mechanism. The annular ring has a diameter greater than the diameter of the butt of the workpiece slightly smaller than the first stepped end of the piston, but less than the largest diameter of the piston. The annular ring prevents the impact of piston on the restricted area of barrel and prevents inadvertent escape of the piston in the event the ring and the restricted area fail.
It is therefore an object of the present invention to provide a piston retaining system that will prevent the free escape of the piston from the barrel of a reciprocal tool when the retaining sleeve and workpiece are removed and the lever is activated inadvertently.
It is therefore a further object of the present invention to provide piston retaining systems that will not interfere with, or contact, the piston or workpiece during normal operation of the tool.